Conventional techniques regarding the current capacity of a television lens are disclosed in, for example, Japanese Patent Laid-Open Nos. 9-304680 and 2000-171875. Japanese Patent Laid-Open No. 9-304680 discloses a television lens apparatus which adopts a switch to set the current limiting value of a camera. When a current having a set value is equal to or smaller than 2 A (ampere), for example, zooming and focusing operations are inhibited during the operation of an extender, thereby stably performing each operation.
Japanese Patent Laid-Open No. 2000-171875 discloses a television lens apparatus which switches the operation limitation stepwise to acceleration limitation, stop immediately before mechanical limitation, inhibition of simultaneous operations, and the like in accordance with the maximum current detection result.
As recent television lens systems become multifunctional, increase the zooming speed, improve the servo performance, and use optional members, power consumption is increasing. Conventional television lens systems deal with an increasing amount of power consumption by connecting an auxiliary power source to a television lens or imposing function restriction, but this is not convenient for the user. Thus, the latest television cameras compensate for current shortage by increasing a supply current to a television lens. For example, the amount of supply current from a television camera to a television lens has generally been 2 A, but models capable of supplying a current up to 3 or 4 A are becoming available.
However, there are only a limited number of television cameras compatible with the above-mentioned television lens consuming a large amount of power. Depending on a combination of a television camera and television lens, functions are restricted though the current supply is sufficient, failing in control fully using the amount of current supply. If a television lens consuming a large amount of current is connected to an incompatible television camera, no sufficient amount of current can be supplied, and the operation of the television lens becomes unstable. In the worst case, the television camera may fail.
Japanese Patent Laid-Open No. 9-304680 discloses a television lens apparatus capable of setting the current limiting value of a mounted television lens. However, every time the television camera on which the television lens is mounted changes, the user needs to cumbersomely confirm the specifications of the television camera and set the current limiting value again. If a set current limiting value is not proper, the television camera may not operate normally, and in the worst case, may fail.
Japanese Patent Laid-Open No. 2000-171875 discloses a television lens apparatus which adopts a current detection circuit in a television lens and can restrict the operation in accordance with the maximum current detection result. However, at least in measurement, a current larger than a current value suppliable from the television camera to the television lens may flow. Further, this reference does not describe the criterion of a peak current. For this reason, the maximum current detection result may exceed a range assured in the television camera.
The current value suppliable from the television camera to the television lens may change depending on the use status of the television camera or the power source state. However, according to the above-described conventional techniques, control of the television lens cannot quickly follow a change of the current capacity. When a plurality of current supply sources exist for the television lens, for example, when an auxiliary power source unit is directly mounted on the television lens, the television lens cannot always be controlled optimally.
Japanese Patent Laid-Open No. 2000-171875 discloses a method of suppressing the current consumption amount by stopping the zoom lens immediately before mechanical limitation. However, if the angle of the television lens changes while the zoom lens stops, the position of the zoom lens may change by its own weight.